I used to install hot high pressure wash systems in fish factories, with Karcher pump units & all piped in 1/2" sched 40 s/s pipe, all tig welded joints. If it was a new factory it was a race to get in first before the plumbers & sparks, it meant you could get more straight runs without having to loop around existing trunking & pipes!
We usually got a pro tig welder in to do the welding but I did a mushroom compost factory myself using mma & a sip buzz box! It was a simple system but I managed it with no leaks!
ohh... I'm planning to run a couple of lines like that at work for the steam cleaners
I was thinking about stainless pipe but didn't know about just using threaded fittings and screwing it all together? - I'm guessing it needs hydraulic fittings on the end which makes a mess of my idea to cut and thread the pipe? .... did you weld all the pipes together opt weld fittings on the end?
if it gets too tricky... I'll just run normal pressure washer hose inside some ducting :-o